Airborne power ultrasonic systems for food dehydration processes intensification

Abstract

Process intensification constitutes a high interesting and promising industrial area. It aims to modify conventional processes or develop new technologies in order to reduce energy needs, increase yields and improve product quality. When drying at low temperature, heat degradation is diminish, although long drying times may induce quality losses and involve high operating costs. It has been demonstrated by this research group (CSIC) that power ultrasound have a great potential in food drying processes. The effects associated with the application of power ultrasound (turbulence, diffusion, acoustic streaming, etc.) can enhance heat and mass transfer and may constitute a way for process intensification. In order to produce the desired effects in the food samples, the ultrasonic system has to generate an intense ultrasonic field with high amplitude levels. These requirements may lead the system to work in a nonlinear regime, both in the generation process (frequency shifts, hysteresis, etc.) and in the acoustic propagation through the gas medium (shock waves, harmonics, etc.). The ultrasonic system, in charge of the generation this specific acoustic field, has to be designed in order to have a resonant mode behavior with a high quality factor and narrow bandwidth. This system is based on a Langevin-type transducer, a mechanical amplifier and an extensive radiator that allows a good impedance matching with the medium, large amplitude of vibration, and high directional beams for energy concentration. The aim of this work is to introduce an ultrasonic system that fulfils those requirements, considering the whole process composed by the numerical simulation using finite element models (FEM), the dynamic and acoustic characterization